(a) Field of the invention
This invention relates to blade type focal plane shutters and more particularly to an improvement of supporting structure for exposure slit forming shutter blades.
(b) Description of the Prior Art
Generally, in a blade type focal plane shutter, each of front blade group and rear blade group consists of a plurality of opaque laminae, one of the laminae is used for form an exposure slit and the remainder are used to cover an exposure aperture.
FIGS. 1 to 3 show an example of conventional focal plane shutter of such type as described above. In the drawings, only a front blade group F is shown but a rear blade group is omitted to simplify the illustration. In FIGS. 1 to 3, reference numeral 1, 2 and 3 denote respectively a shutter base plate, intermediate plate and cover plate which are integrally combined with one another at proper intervals through connecting members not illustrated and in which exposure apertures 1a, 2a and 3a aligned with one another are respectively formed. Reference numeral 4 denotes a main arm which is pivoted in the base portion on the base plate 1 through a shaft 5 and has pins 4a, 4b and 4c erected respectively in the tip portion and intermediate portion. 6 denotes an auxiliary arm which is pivoted in the base portion on the base plate 1 through a shaft 7 and has a pin 6a erected in the tip portion. 8 denotes a main rectangular lamina which is pivoted on the arms 4 and 6 respectively through the pins 4a and 6a, has an end edge 8a for forming an exposure slit and is made of such material high in the specific gravity and strength as steel. As the pivots 5, 7, 4a and 6a are so arranged that the line segments connecting their center points may form a parallelogram, the end edge 8a will move always in parallel with the long sides of the exposure apertures 1a, 2a and 3a. Reference numeral 9 denotes an auxiliary lamina which is arranged just below the lamina 8, has a cam slot 9a formed in the base portion so as to slidably fit the pin 4b, is pivoted in the intermediate portion to the auxiliary arm 6 through the pin 6a, extends in the tip portion 9b over the exposure apertures 1a, 2a and 3a and is made of the same material as of the lamina 8. Reference numerals 10, 11, 12 and 13 denote auxiliary laminae which are arranged in turn below the lamina 9, are pivoted in the respective base portions on the intermediate plate 2 through a shaft 14, have slots 10a, 11a, 12a and 13a formed in the respective intermediate portions so as to slidably fit the pin 4c, extend in the respective tip portions over the exposure apertures 1a, 2a and 3a and are made of the same material as of the lamina 9. The laminae 9, 10, 11, 12 13 are so arranged that respective two adjacent ones may partly overlap each other to be used to cover the exposure apertures 1a, 2a and 3a together with the lamina 8 when they are unfolded as shown in FIG. 1 and that they may be contained as mostly overlapped in a space formed by the base plate 1 and intermediate plate 2 in a position retreated from the exposure apertures 1a, 2a and 3a when they are folded as shown in FIG. 3.
The formation of the front blade group F has been explained in the above. In fact, a rear blade group consisting of six laminae is arranged in a space formed by the intermediate plate 2 and cover plate 3 so as to be in a mirror image relation with the front blade group F so that the rear blade group may be folded in a position retreated upward of the exposure apertures 1a, 2a and 3a when the front blade group F is unfolded as shown in FIG. 1 and may be unfolded to cover the exposure aperture 1a, 2a and 3a when the front blade group F is folded as shown in FIG. 3.
The operation shall be explained in the following:
In the cocked state in FIG. 1, when the shutter is released, the main arm 4 will be quickly rotated clockwise by a driving spring or driving member not illustrated. At this time, the auxiliary arm 6 will be simultaneously rotated clockwise through the lamina 8 and therefore the end edge 8a of the lamina 8 will lower to the position in FIG. 3 while remaining in parallel with the long sides of the exposure apertures 1a, 2a and 3a. On the other hand, the lamina 9 will be rotated clockwise to the position in FIG. 3 by the auxiliary arm 6 while being restrained in the base portion by the connection of the pin 4b with the cam slot 9a and the laminae 10, 11, 12 and 13 will be rotated clockwise to the positions in FIG. 3 around the shaft 14 by the connection of the pin 4c with the cam slots 10a, 11a, 12a and 13a. In this case, the respective laminae 12, 11, 13, 10, 9 and 8 will reach the positions in FIG. 3 in the order mentioned while increasing the overlap with each other, therefore, when the lamina 8 retreats from the exposure apertures 1a, 2a and 3a, the exposure apertures will be fully opened and, during the movement, the respective laminae will not collide with each other. In fact, when the lamina 8 retreats from the exposure apertures as described above or opens a part of the exposure apertures, the folded rear blade group will advance into the exposure apertures 1a, 2a and 3a to cover them. Therefore, it is needless to say that the exposure apertures will result in being opened only during a set time.
The shutter is cocked by rotating the main arm 4 counterclockwise from the position in FIG. 3 to the position in FIG. 1 by means of a winding mechanism not illustrated. In this case, the front blade group F will be unfolded simultaneously with folding the rear blade group and therefore the exposure apertures 1a, 2a and 3a will not be opened.
By the way, recently, it is required to make cameras small. In the focal plane shutter of the above mentioned structure, the height of the base plate 1, intermediate plate 2 and cover plate 3, that is to say, the width of them in vertical direction will have to be made made as small as possible to fulfill this requirement. Further, to make them small, the number of opaque laminae which form the front and rear blade groups will have to be increased as much as possible and the width of the respective lamina in vertical direction will have to be made as small as possible.
However, in the conventional blade supporting structure as described above, if the width of the respective lamina in vertical direction is made small, the distance between the pins 4a and 6a for pivotably supporting the main lamina 8 will also shorten. This results in the unstable support of the main lamina 8 and will make it difficult to move the end edge 8a for forming an exposure slit in parallel with the horizontal edge of the exposure apertures 1a, 2a and 3a. Therefore, there is a limit to making the width of the main lamina 8 in the vertical direction small.
Further, in the conventional blade supporting structure as described above, the distance between the pivots 5 and 7 of the arms 4 and 6 must be equal to the distance between the pins 4a and 6a. Therefore, there is also a limit to making the distance between the pivots 5 and 7 short as apparent from the above mentioned reason. This will make it difficult to make the shutter small.